Low-density sealing mass, ground mass and method for producing the same and the use thereof

ABSTRACT

The invention relates to a sealing mass with low density and improved tensile strength on the basis of sulfur-containing polymers such as on the basis of polysulfide, polyether or/and polytioether that has a density of not more than 1.3 g/cm 3  according to ISO 2781 and a tensile strength of at least 1.9 N/mm 2  according to ISO 37 after curing. The invention further relates to a ground mass based on sulfur-containing polymers for producing a sealing mass that comprises at least one long-chain linear polymer and at least one short-chain branched polymer having a content in trifunctional molecules, or/and at least one multifunctional cross-linker with a number of functional groups n≧3. The invention further relates to a method for producing a sealing mass according to which at least one base polymer is mixed with at least one adhesion promoter and the at least one light filler, especially hollow filler, is added, a vacuum with a remaining pressure of less than 50 mbar being maintained during incorporation of the light filler.

[0001] The invention relates to a low-density sealing composition withincreased tensile strength based on sulfur-containing polymers and alsoan accompanying base composition and a process for their manufacture.

[0002] The-sealing composition of the invention is intended to serve inparticular for the bonding or gluing of parts and/or the sealing orfilling of cavities and interstices. This is of particular interest inaviation and space travel, but also anywhere where, as a result of alarger quantity of sealing compositions, particular attention must bepaid to the weight used, in other words to the density of the sealingcompositions, as e.g. with land vehicles.

[0003] Sealing compositions are now used for the widest variety ofapplications. They serve in particular for the sealing of constructionelements, the gluing e.g. of sheets to existing structures such as e.g.sections of an aircraft or to protect against corrosion in areas wherethe anti-corrosion layers of metal elements have been damaged or removede.g. in the vicinity of drill holes and may temporarily assume asupporting function e.g. during the transport of structures underconstruction, which are subsequently fitted with permanent supportingjoining elements.

[0004] In principle, two process variants are-possible for manufacturinglow-density sealing compositions: Either hollow filling bodies are usedwhich, as a result of a gas-filled cavity, are manufactured with a verylow density. Or fillers in compact form can be added which, as a resultof their low density in comparison with the density of the othercomponents of the sealing composition, such as e.g. inorganic fillers,are particularly light and thus help to reduce the density overall.However, to the knowledge of the applicant, the production oflightweight sealing compositions has reached its limit at a minimum of1.30 g/cm³, as the base polymer itself has a density in the range of 1.0to 1.3 g/cm³ and as the fillers used hitherto have a densityapproximately in the range of 2 to 4 g/cm³.

[0005] Particular demands are now made of sealing compositions for theproduction and maintenance of-air- and spacecraft. As a result of theiruse in the sealing of fuel tanks, protection against corrosion,aerodynamic smoothing and sealing of the pressure hull, great emphasisis placed on elasticity over a wide temperature range, resistance tovarious media such as e.g. fuel, hydraulic fluid, condensation andanti-freeze fluid and a good sealing and bonding action on the widestvariety of substrates.

[0006] In addition, in the case of interlayer sealing compositions, itis desirable that such compositions have no hollow bodies or cavities.

[0007] It can be assumed that ca.1000 to 2000 kg sealing compositionsare used in the construction of an airliner. If, therefore, the densityof these sealing compositions could be reduced by e.g. 10 to 30%, thiswould result in a tangible reduction in weight: e.g. from a density ofca.1.5 g/cm³ to ca.1.28 g/cm³ or in some cases even to ca.1.1 g/cm³.

[0008] U.S. Pat. No. 5,663,219 discloses a sealing composition based onpolysulfide, the sealing composition having a density in the range 1.0to 1.3 g/cm³ and a peel strength in the range above 17 pounds per linearinch. This specification gives a density below 1.3 g/cm³ only once inthe examples, namely 1.1 g/cm³ in example 1, but gives no furthermechanical typical data for this. On the basis of the remaining data andknowledge of the formulations, it is assumed that the peel strength ofthis sealing composition is rather low. The best average value given forpeel strength, which is given for example 10, is 28.3 pounds per linearinch (a 124 N/25 mm). No tensile strength data are given for this.

[0009] The object was therefore to propose a sealing composition with aslow a density as possible, but at the same time with good mechanicalproperties and a manufacturing process for these sealing compositionsthat is as simple as possible, and that can be manufactured withpolymers that are as economic as possible and that also has a widevariety of applications. Above all, these sealing compositions shouldalso be extremely suitable for use in aerospace applications.

[0010] The object is achieved by a sealing composition of low densityand increased tensile strength based on sulfur-containing polymers suchas e.g. on polysulfide, polyether and/or polythioether, which ischaracterised in that it has a cured density of no more than 1.3 g/cm³determined to ISO 2781 and a tensile strength of at least 1.9 N/mm²determined to ISO 37.

[0011] For the sake of linguistic simplicity, the term sealingcomposition in the context of this invention is used below in some casesin such a way that it comprises, in addition to the cured sealingcomposition, also the concept of the base composition and the basecomposition when mixed with the hardener (e.g. based on manganesedioxide with accelerators, wetting agents etc). The term basecomposition describes a mixture which after mixing with the hardener andafter curing with the hardener is normally understood to be a sealingcomposition. A content of hardener in relation to base polymer in therange of 5:100 to 15:100 is mostly used.

[0012] The sulfur content of the sealing compositions according to theinvention may already be contained in the base polymer—e.g. in thepolysulfide, polythioether or polyether with individual sulfur bridges(as single and/or double bridges), or may be introduced by means of theterminal mercapto groups. The base composition comprises the basepolymer of the sealing composition according to the invention, intowhich the other components are mixed or have been mixed. The proportionof the base polymer in the total sealing composition is conventionally50 to 85 wt. %, preferably 55 to 82 wt. %, particularly preferably 62 to78 wt. %. A higher proportion of fillers and/or hollow filling bodies isto be added to the base polymer, on the one hand to reduce the densityas far as possible and on the other to set the highest possiblemechanical properties. The base polymer mostly has a density in therange of 1.0 to 1.4 g/cm³, in the case of the polysulfide base polymerapproximately of 1.29 g/cm³. The chain length of the base polymer maypreferably be in the range of 1000 to 8000 g/mol, particularlypreferably in the range of 2000 to −5000 g/mol, most preferably in therange of 2500 to 4500 g/mol. The chains of the base polymer may bepurely linear or crosslinked to a limited extent. The proportion ofcrosslinking is preferably 0 to 90%, in particular 20 to 80%, mostparticularly at least 40% or up to 70%, in each case in relation to thenumber of the chains, the molecular weight in relation to the percentageby weight being taken into account.

[0013] Surprisingly, it was found that at least one long-chain linearpolymer (e.g. at least one linear polysulfide with a chain length in therange approximately of 1500 to 5000 g/mol, in particular in the rangeapproximately of 2000 to 4500 g/mol such as e.g. LP 541 from Rohm & Haasor G 10 from Akzo Nobel) in combination with at least one short-chain,branched polymer (e.g. at least one branched polysulfide with a chainlength in the range approximately of 500 to 2000 g/mol, preferably inthe range approximately of 800 to 1500 g/mol, in each case with acontent of trifunctional molecules in the range of 0.1 to 5 mol %, inparticular with a content in the range of 0.5 to 2-mol %, such as e.g.LP 3, LP 33 from Rohm & Haas or G 44, G 4 from Akzo Nobel) and/or atleast one polyfunctional crosslinker—optionally partially or wholly as asubstitute for the short-chain polymers—with the number of functionalgroups n>3, produces particularly good mechanical properties. Preferablyn=3 and/or 4, but in principle can also take on values of n=3, 4, 5, 6,7 and/or 8, but rarely values for n greater than 8. The polyfunctionalcrosslinker may be mercapto-functional e.g. as in the case ofpentaerythritol-tetrakis-3-mercaptopropionate, trimethylolpropanemercaptopropionate or trimethylolpropane trimercaptoacetate from BrunoBock, or epoxy-functional as in the case of the triglycidyl propylaminophenol TGPAP from Shell, Araldit® MY 0500 and Araldit® XU MY 0505 fromCiba or DEN 431 from Dow. The content of crosslinkers may vary from 0 to5 wt. %, preferably, where crosslinkers are added, 0.1 to 3 wt. %,particularly preferably no more than 0.5 wt. %. The chemical variants ofthe base polymer and the crosslinker are known in principle to theperson skilled in the art.

[0014] In addition, the base composition may contain at least oneadhesion promoter. This serves to bind the fillers and hollow fillingbodies into the polymer and to aid adhesion to the substrate. Whereused, it is normally contained in a total quantity of 0.1 to 8 wt. %.

[0015] Furthermore, the base composition-may contain at least onemineral filler. This may be a filler e.g. based on aluminium oxide,aluminium hydroxide, chalk, silica, silicates and/or sulfates. The totalcontent of these may vary from 0 to 49 wt. %, preferably 1 to 40 wt. %,particularly preferably at least 2 wt. % or up to 30 wt. %, mostparticularly preferably at least 5 wt. % or up to 25 wt. %.

[0016] Furthermore, where needed, it may contain in particular at leastone each of a rheological additive to establish e.g. the thixotropyand/or the flow properties, a biocide, a corrosion inhibitor or anadditive with a different action.

[0017] In addition, the object was achieved with a base compositionbased on sulfur-containing polymers for the manufacture of a sealingcomposition, which is characterised in that it contains at least onelong-chain linear polymer, in particular at least one linear polysulfidewith a chain length in the range for instance of 1500 to 5000 g/mol, andat least one short-chain, branched polymer, in particular at least onebranched polysulfide with a chain length in the range approximately of500 to 2000 g/mol, which has a content of trifunctional molecules, inparticular in the range of 0.1 to 5 mol % and/or at least onepolyfunctional crosslinker with the number of functional groups n≧3.Instead of the content of trifunctional molecules, higher-functionalmolecules may in principle also be used at the same time or as analternative in particular up to n=8. The linear polysulfide preferablyhas a larger proportion, largely or even wholly, of a linear chain witha functionality of 2, i.e. two terminal functional groups.

[0018] Furthermore, the object was achieved with a base compositionbased on sulfur-containing polymers for the manufacture of a sealingcomposition, which has a density before the addition of a hardener notexceeding a value of 1.285 g/cm³, in particular a value of up to 1.28g/cm³, preferably a value of up to 1.26 g/cm³, most preferably of up to1.23 g/cm³, above all a value of up to 1.18 g/cm³, in particular a valueof up to 1.12 g/cm³.

[0019] The density e.g. of the liquid base polymer can be measured as atrue density on a pycnometer to DIN 53479 of July 1976. The density ofthe cured sealing composition can be determined to ISO-2781 of December1988 using a minimal quantity of a surfactant in distilled wateraccording to the Archimedes principle. If the cured sealing compositioncontains hollow filling bodies, its density may lie in the range of 0.8to 1.29 g/cm³, preferably in the range of 0.85 to 1.27 g/cm³, inparticular in the range of 0.9 to 1.24 g/cm³, above all in the range of0.95 to 1.20 g/cm³.

[0020] The tensile strength was measured on dumb-bell-shaped test bodiesof cured sealing composition of the size of Type 2 with a tension speedof 500 mm/min to ISO 37 of May 1994 in a Universal test machine. Thetensile strength may be at least 2.0 N/mm², preferably at least 2.05N/mm², particularly preferably at least 2.15 N/mm², above all at least2.25 N/mm² (=MPa).

[0021] The sealing composition according to the invention may also havea peel strength of at least 90 N/25 mm, preferably of at least 125 N/25mm. The peel strength represents the internal strength and in particularthe adhesion of a cured sealing composition to substrates.

[0022] It was determined on specimens of cured sealing composition toAITM 2-0013 with special steel wire cloth.

[0023] Surprisingly high values for peel strength and at the same timehigh values for tensile strength were achieved, even without addingepoxidated polysulfides such as e.g. ELP-3 (given in U.S. Pat. No.5,663,219). If a sealing composition according to the invention ismanufactured with an epoxidated polysulfide (=polysulfide with terminalfunctional epoxide groups, so that there is no mercapto functionality),no positive influences on tensile strength are produced to the knowledgeof the applicant.

[0024] Surprisingly however, it was found that high tensile strengthscombined with high peel strength values can be achieved at low densitieseven without the use of special polymers such as e.g. Permapol® P-5 orepoxidated polysulfides. However, both the epoxidated polysulfides andthe special polymers such as e.g. Permapol® P-5 are significantly moreexpensive than conventional polysulfides, as they require a laboriousadditional production step. It is therefore advantageous that unmodifiedpolysulfides are sufficient for most of the sealing compositionsaccording to the invention.

[0025] The sealing composition according to the invention may contain aproportion of lightweight polymeric strength-increasing filler such ase.g. polyamide, polyethylene, polypropylene. This filler is preferablyadded in powder form, optionally as a mixture of at least two differentfillers. The average particle size of the filler powder may be in therange of 0.5 to 80 μm, preferably in the range of 1 to 40 μm,particularly preferably in the range of 1.2 to 30 μm, most preferably inthe range of 1.5 to 20 μm. It may be advantageous to use a powder thathas been surface-modified e.g. by corona treatment or by anotheractivating treatment such as e.g. treatment of the filler surface withsilanes. Surface modification can achieve an improved bonding of thepolymeric powder into the sealing composition and thus improvedmechanical properties. Functional groups which facilitate bonding intothe base polymer, such as e.g. polysulfide, should thus be madeavailable on the surface of the powder particles. The proportion oflightweight polymeric strength-increasing filler, where this is nothollow filling bodies, may amount to 0 to 35 wt. %, the hollow fillingbody-free sealing compositions preferably having 10 to 25 wt. %,particularly preferably 14 to 22 wt. %. If at least one type each ofhollow filling bodies and lightweight polymeric strength-increasingfillers is used simultaneously, the sum of the contents is 0.3 to 35 wt.%, preferably 5 to 20 wt. %.

[0026] The density of the sealing composition according to the inventionmay, without a proportion of hollow filling bodies, be no more than 1.30g/cm³. A density of no more than 1.28 g/cm³ is preferably achieved,particularly preferably a density of no more than 1.26 g/cm³. Thedensity of the base composition according to the invention may, withouta proportion of hollow filling bodies, have a value of no more than1.285 g/cm³, in particular a value of up to 1.28 g/cm³, preferably avalue of up to 1.27 g/cm³, most preferably of up to 1.25 g/cm³, aboveall a value of up to 1.22 g/cm³, in particular a value of up to 1.19g/cm³.

[0027] The true density of these fillers, without taking account ofhollow filling bodies, normally lies approximately in the range of theaccompanying polymers and thus mostly in the range approximately of 0.8to 1.3 g/cm³. The polymeric filler powders may have a true density inthe range of 0.5 to 1.5 g/cm³. The inorganic filler powders may have atrue density in the range of 0.18 to 4.5 g/cm³. The latter powders may,in some cases, have a closed porosity. The density of the fillers, whichare not hollow filling bodies, may be determined to DIN 53479 of July1976 using a minimal quantity of a surfactant in de-gassed deionisedwater in a pycnometer.

[0028] The density of the hollow filling bodies may be determined in asimilar way, however using a graduated measuring cylinder with a notchedplunger, which is pressed onto the surface of the volume of watercontaining the hollow filling bodies to remove the contained air, themeasuring cylinder which is closed with the notched plunger having beenshaken previously to disperse the hollow filling bodies whilst avoidingfoam formation.

[0029] The sealing composition according to the invention may have aproportion of hollow filling bodies such as e.g. polymeric hollowspheres in the range of 0.3 to 10 wt. %. The proportion of hollowfilling bodies is preferably in the range of 0.5 to 5 wt. %. Here aproportion of e.g. 2 wt. % hollow filling bodies may constitute aproportion by volume of the sealing composition in the range of 15 to 35vol. %, depending on the type of hollow filling body. The addition ofhollow filling bodies helps to reduce the density of the sealingcomposition relatively significantly because of the extraordinarily lowtrue density of the hollow filling bodies.

[0030] The sealing composition according to the invention may havehollow filling bodies with an average diameter of no more than 50 μm, inparticular those of no more than 30 μm, measured under a lightmicroscope, the particles lying largely scattered on the slide.

[0031] The hollow filling bodies may have a true density in the range of0.001 to 0.8 g/cm³. The true density is preferably 0.01 to 0.6 g/cm³,particularly preferably 0.02 to 0.3 g/cm³. Hollow filling bodies may, inprinciple, consist of any material and may optionally additionally becoated. They preferably consist substantially of a ceramic material, ofglass or of an organic material such as e.g. of an aluminium-containingsilicate. In particular, they consist substantially of a polymericmaterial e.g. based on acrylonitrile copolymer or methacrylonitrilecopolymer. The shape of the hollow filling bodies is preferablysubstantially spherical. The average diameter of the hollow fillingbodies is preferably in the range of 2 to 100 μm, in particular in therange of 5 to 45 μm.

[0032] Here, lightweight filling bodies and optionally also fillers withan average particle size of no more than 30 μm, preferably of no morethan 20 μm, may be used to achieve better spreadability and mouldabilityof the sealing composition during processing.

[0033] If the average diameter of the hollow filling bodies is toolarge, the sealing composition will no longer be homogeneously composedand accordingly will form inhomogeneous surfaces on curing, whichrestricts possible applications, or the sealing composition will notachieve the desired high mechanical properties. The wall thickness ofthe hollow filling bodies may vary significantly, but is preferably low,to produce a lower density of the sealing composition. Astonishingly,even extremely thin-walled hollow filling bodies have scarcely ever beenpulverised in spite of severe mechanical attack during mixing of theindividual components of the sealing composition. The hollow fillingbodies are preferably filled with air, certain gases such as e.g.nitrogen or carbon dioxide, isobutane, n-pentane, isopentane and/orother waste gases from the manufacturing process.

[0034] The density of the sealing composition according to the inventionthat contains hollow filling bodies may lie in the range of 1.3 to 0.7g/cm³, in particular in the range of less than 1.28 g/cm³, preferablyless than 1.25 g/cm³, particularly preferably less than 1.22 g/cm³,particularly preferably less than 1.18 g/cm³, in particular less than1.12 g/cm³, above all less than 1.06 g/cm³.

[0035] If a suitable base polymer, adhesion agent and polymeric fillerare selected, surface modification of the polymer powder is notnecessary, although it could be beneficial, because a certain level ofstrength is already achieved as a result of this selection. When addingthe hollow filling bodies, the addition of structure-forming inorganicfillers for the formation of good mechanical properties is preferred tothe use of the polymeric filler powders. The surface properties of thepolymeric filler powders have a far greater influence on the quality ofthe sealing compositions produced with them than the selection of thechemical type of the polymer of the polymeric filler powders.

[0036] However, in most cases, the higher the tensile strength selectedfor such sealing compositions, the lower the peel strength of thesesealing compositions. Surprisingly, it was found that this opposingcorrelation can be avoided to a greater extent only if the sealingcomposition is manufactured by the process according to the invention.

[0037] The composition of the sealing composition according to theinvention is otherwise known in principle. The sealing compositionaccording to the invention may, before and after curing, additionallycontain a corrosion inhibitor, in particular a chromate-free corrosioninhibitor.

[0038] For aerospace applications, it is extremely important to complywith the requirements of the specifications AIMS 04-05-001 GeneralPurpose Specification, AIMS 04-05-002 Fuel Tank Specification and wherepossible also the more stringent Fuel Tank Specification AIMS-04-05-012.To the knowledge of the applicant, it is extremely difficult to fulfilthe minimum tensile strength requirement of 2.0 N/mm² determined to ISO37 of May 1994 in the Airbus Industries Material SpecificationAIMS-0405-012. Furthermore, achieving, the minimum peel strength of thecured sealing composition of 120 N/mm² after one thousand hours'immersion in deionised water at 35° C. in accordance with AIMS-04-05-012of November 1997 determined to AITM 2-0013 of June 1995 is problematic.It is also difficult to achieve the minimum peel strength of the curedsealing composition of 120 N/mm after three periods of one hundred hourseach of immersion in jet fuel DERD 2494 at 100° C. according toAIMS-04-05-012 determined to Airbus Industries Test Method AITM 2-0013.Most of the sealing compositions according to the invention even fulfilall of the requirements of all these specifications. This includes alsoa minimum tensile strength of 2.0 N/mm² determined to ISO 37 of May 1994in combination with a peel strength {circumflex over ( )}(Peel) of atleast 120 N/25 mm determined to AITM 2-0013 of June 1995 and incombination with a density of up to 1.30 g/cm³ determined to ISO 2781 ofDecember 1988.

[0039] To the knowledge of the applicant, no single fully cured sealingcomposition has hitherto actually fulfilled all of the requirements ofthe specification AIMS 04-05-001 of November 1996 and also AIMS04-05-012 of November 1997, which are significantly higher than those ofAIMS 04-05-002 of November 1996.

[0040] The cured sealing composition according to the invention canfulfil low-temperature flexibility at −55° C. determined to ISO 1519.This is determined by bending a sheet coated with sealing compositionover a mandrel, during which process the sealing composition must remaincrack-free; the mandrel has a diameter of 10 mm.

[0041] The cured sealing composition according to the invention can havea peel strength of at least 120 N/mm after one thousand hours' immersionin deionised water at 35° C. determined to AITM 2-0013.

[0042] The cured sealing composition according to the invention can havea peel strength of at least 120 N/MM2 after three periods of one hundredhours each of immersion in jet fuel DERD 2494 at 100° C., determined toAITM 2-0013.

[0043] The cured sealing composition according to the invention canfulfil all the requirements of the specifications AIMS-04-05-001 andAIMS-04-05-012. It preferably fulfils all the requirements of thesespecifications, whilst also exceeding numerous limits such as density,tensile strength and peel strength as stated.

[0044] The object is also achieved by a process for the manufacture of asealing composition, which is characterised in that at least one basepolymer is mixed with at least one adhesion promoter and then the atleast one lightweight filler, in particular hollow filling bodies, isadded, a vacuum with a residual pressure of less than 50 mbar,preferably less than 10 mbar, being applied when working in thelightweight filler.

[0045] All or some of the other fillers and/or crosslinkers and furtheradditives may each be added before and/or after the at least onelightweight filler is mixed in. With the other fillers however, it ispreferable for at least part of them to be added only after mixing inthe at least one lightweight filler. It may be advantageous if thosefillers that are not readily wettable, and/or have a particularly largespecific surface area, are added before the addition of the lightweightfillers and mixed with the polymers, but that those that are readilywettable, and/or have a comparably small specific surface area, are notadded and intermixed until afterwards.

[0046] Mixing may in principle be carried out in one or more units inseries. Here it is important that the base polymer and adhesion promoterare first mixed homogeneously with each other and lightweight fillingbodies are then admixed. The air content of the mixture thus formed mustbe removed as fully as possible, to achieve good wetting and intermixingof the individual components. Evacuation may take place, if necessary,in another unit. However, it is advantageous to mix intensively andevacuate at the same time. To remove as much as possible of the airadhering to the lightweight fillers and to wet the lightweight fillersas well as possible with the base polymer and the adhesion promoter.Surprisingly it was found that the mechanical stability of the hollowfilling bodies is so great that they can be mixed and worked in evenwith particularly severely and rapidly attacking mixing units, such ase.g. a dissolver, in particular a vacuum dissolver, at a high speed,without being destroyed.

[0047] With the process according to the invention for the manufactureof a sealing composition, the lightweight filler can be worked in in alaboratory scale vacuum dissolver at a peripheral toothed disc speed inthe range of at least 2 m/s, in particular of at least 3 m/s,particularly preferably in the range of 5 to 15 m/s. With the processaccording to the invention for the production of a sealing compositionthe lightweight filler can be worked in in a production scale vacuumdissolver at a peripheral toothed disc speed in the range of at least 5m/s, in particular of at least 10 m/s, particularly preferably in therange of 12 to 30 m/s. Astonishingly, the hollow filling bodies were notdestroyed even with a very severe attack in the range of 18 to 22 m/s,but were so well wetted and homogeneously worked in that the mechanicalproperties of the sealing composition formed significantly improved incomparison with lower peripheral speeds and also with alternativeconventional processes for the manufacture of such sealing compositions.

[0048] In the process according to the invention, the other componentsof the sealing composition can then be introduced and intermixed andevacuation can optionally take place during and/or after this process.

[0049] The non-cured or cured sealing composition according to theinvention can be used in particular for the construction and maintenanceof air- and spacecraft and for motor and rail vehicles, in shipbuilding,in apparatus engineering and mechanical engineering, in construction andcivil engineering or for the manufacture of furniture.

EXAMPLES

[0050] The subject of the invention is explained in more detail belowwith the aid of embodiments.

[0051] General manufacturing instructions for the lightweight sealingcompositions:

[0052] First the base polymers Thioplast® G 10 and Thiokol® LP 33 andthe adhesion agents Methylon Resin 75108 and Nafturan® 8187 wereprovided. After the addition of lightweight fillers such as e.g.Acumist®, Dualite®, Expancel®, Rilsan® and/or Vestosint® and Aerosil® R202 as a structure-providing filler, the components were mixed for 5minutes under full vacuum (<50 mbar, if possible <10 mbar) in adissolver at a peripheral speed of ca. 3 m/sec. The chalk Winnofil® SPTor Polcarb® S was then added as a structure-providing filler and thebase composition was dispersed for 10 minutes at a peripheral speed ofca. 3 m/sec under vacuum (<50 mbar, if possible <10 mbar). The vacuumwas applied slowly and mixing continued until as much as possible of thewaste gases had been drawn off, which could be recognised also by thefact that after a significant increase in volume, the base compositioncollapsed again.

[0053] If the recipe provides for the addition of deionised water, acooling phase of 5 minutes followed, in which the material was stirredwhilst cooling under full vacuum (<50 mbar, if possible <10 mbar) at aperipheral speed of ca.1 m/sec. In the final step, deionised water wasadded after cooling and homogenisation took place for 5 minutes at aperipheral speed of ca.1 m/sec and a negative pressure of 400 to 600mbar with renewed cooling. The base compositions were then left to standfor at least 1 day, before they were ready for use.

[0054] To manufacture the test bodies, the hardener Naftoseal® MC-238B-2 was added to the relevant base composition at a ratio of 100:10 andthe two were mixed homogeneously, so that they formed a sealingcomposition. After curing, i.e. after 14 days at 23° C. and 50% relativehumidity in air, the properties of the test bodies were determined. Theywere determined as stated previously in the description.

[0055] Test Series A:

[0056] This test series illustrates the influence of the manufacturingprocess. The base and sealing compositions according to the inventionwere manufactured according to the instructions given above, whilst thereference examples were manufactured according to the conventionalmanufacturing method: TABLE 1 Specific density and average particlesizes of the lightweight fillers used according to the manufacturers'data Specific density Average particle size Lightweight filler g/cm³ μmAcumist ® A-6 0.99  6 Rilsan ® D 30 naturelle 1.04 20-30 Vestosint ®2070 1-1.2  5 Vestosint ® S 7126 1-1.2 Not determined Expancel ® 551 DE20 0.06 15-25 Expancel ® 461 DE 0.06 20-40 Dualite ® 6033 0.13 25Dualite ® 6032 0.13 70 Expancel ® 091 DE 0.03 35-55

[0057] The first four lightweight fillers belong to the class of polymerpowders, the rest to the class of hollow filling bodies. The polymerpowders were used in test series B and the hollow filling bodies in testseries A and C. Aerosil® R 202, Polcarb® S and Winnofil® SPT are mineralfillers. TABLE 2 Recipes for an improved manufacturing process in wt. %Raw material Ex 1 Ex 2 Ex 3 Ex 4 1. Thioplast ® G 10 74.78 74.78 74.7874.78 2. TTMA 0.21 0.21 0.21 0.21 3. Methylon Resin 75108 1.60 1.60 1.601.60 4. Nafturan ® 8187 1.64 1.64 1.64 1.64 5. Polcarb ® S 18.29 18.2918.29 18.29 6. Aerosil ® R 202 1.78 1.78 1.78 1.78 7. Expancel ® 551 DE20 1.68 1.68 1.68 1.68

[0058] Manufacturing Process for Ex 1:

[0059] The base composition without lightweight filler was manufacturedin the conventional way, so that first all liquid components and thenall fillers except the lightweight fillers are added, mixing andevacuation being carried out in between and/or at the end. Thelow-density filler was then added and was intermixed at a peripheralspeed of ca.1 m/s. The material was then de-aerated at a residualpressure of ca.200 mbar.

[0060] Manufacturing Process for Ex 2:

[0061] The base composition without lightweight filler was manufacturedin the conventional way as for Ex 1. The low-density filler was thenadded and intermixed at a peripheral speed of ca.1 m/s. The material wasthen deaerated at a residual pressure of <50 mbar.

[0062] Manufacturing Process for Ex 3:

[0063] All components were added in weighed portions, withoutintermediate mixing and were then dispersed for 15 minutes at aperipheral speed of ca.3 m/s and at a vacuum of well below 50 mbar.

[0064] Manufacturing Process for Ex 4:

[0065] The composition was manufactured according to the independentprocess claim of the invention, which means that the base polymer basedon long-chain linear polysulfide Thioplast® G 10 was added with theadhesion promoters Methylon Resin 75108 and Nafturan® 8187 and mixed andthe lightweight filler Expancel® 551 DE 20 (=hollow filling body) andthe filler Aerosil® R 202 were then added, a vacuum with a residualpressure well below 50 mbar and a peripheral speed of ca. 3 m/s beingapplied whilst the lightweight filler was worked in. The remainingcomponents (see table 2) were then added and mixed under a vacuum ofwell below 50 mbar and at a peripheral speed of ca. 3 m/s. TABLE 3Results of the measurements on the reacted sealing compositions for animproved manufacturing process Test Ex 1 Ex 2 Ex 3 Ex 4 Density [g/cm³]1.06 1.08 1.10 1.09 Tensile strength [N/mm²] 1.95 2.34 2.35 2.39Elongation [%] 291 381 413 413 Peel 14 d RT [N/25 mm] 178 188 195 224

[0066] These tests showed that Ex 4, which is according to the inventionnot only as a result of the properties of the cured sealing composition,but also as a result of the manufacturing process, achieved the bestphysical properties of the cured sealing compositions in test series A.

[0067] Surprisingly, the new manufacturing process, above all the highnegative pressure and intensive wetting of the lightweight fillers withthe base polymer and with the adhesion promoter, had a significantinfluence on the properties of the cured sealing compositions.

[0068] Test Series B:

[0069] This test series illustrates the manufacture of base-and sealingcompositions using polymeric powders as lightweight fillers. The sealingcompositions were manufactured according to the manufacturinginstructions according to the invention in the same way as Ex 4, otherchemical components being used in some cases. TABLE 4 Recipes usingpolymeric lightweight fillers with addition quantities in wt. % Rawmaterial Ex 5 Ex 6 Ex 7 Ex 8 Ref 1 Thioplast ® G 10 50.11 52.00 49.6751.81 49.57 Thiokol ® LP 33 20.00 17.48 19.87 17.41 19.84 Methylon Resin75108 1.62 1.62 1.84 1.61 1.61 Nafturan ® 8187 1.50 1.50 1.49 1.49 1.49Acumist ® A-6 8.50 17.00 — — — Rilsan ® D 30 naturelle 9.80 — 19.58 — —Vestosint ® 2070 — — — 16.93 — Vestosint ® S 7182 — — — — 19.84Winnofil ® SPT 7.70 9.00 6.16 8.96 5.46 Aerosil ® R 202 1.40 1.40 1.391.39 1.79 Water — — — 0.40 0.40

[0070] TABLE 5 Results of measurements on the reacted sealingcompositions manufactured according to the formulations of Table 4 TestEx 5 Ex 6 Ex 7 Ex 8 Ref 1 Density [g/cm³] 1.28 1.26 1.30 1.30 1.32Tensile strength [N/mm²] 2.24 2.10 2.41 2.00 1.76 Elongation [%] 285 288282 283 292 Peel 14 d RT [N/25 mm] 190 263 126 262 135

[0071] It was surprising that, in spite of the comparatively smallproportions of reinforcing mineral fillers (Aerosil® R 202 and Winnofil®SPT), high tensile strengths could still be achieved.

[0072] Surprisingly it was found that in addition, the sealingcompositions filled only with small proportions of reinforcing mineralfillers and otherwise with polymer powders also achieved good adhesionto a wide variety of substrates (metals, a wide variety of lacquers) inconjunction with high mechanical typical values.

[0073] Although the base polymer had a density of ca.1.28 g/cm³, theexamples according to the invention of test series B were found, asexpected, to have a sealing composition density of ≦1.30 g/cm³ evenwithout the use of hollow filling bodies.

[0074] Test Series C:

[0075] This test series illustrates the manufacture of base or sealingcompositions using polymeric hollow filling bodies as lightweightfillers. The sealing compositions were manufactured according to themanufacturing instructions according to the invention in the same way asEx 4, other chemical components being used in some cases. TABLE 6Recipes using polymeric hollow filling bodies with addition quantitiesin wt. % Raw material Ex 9 Ex 10 Ex 11 Ex 12 Ex 13 Ref 2 Ref 3Thioplast ® G 10 50.11 55.65 55.38 54.01 74.78 54.01 55.80 Thiokol ® LP33 20.00 19.95 19.85 19.36 — 19.36 20.00 TPTMP — — — — 0.28 — — MethylonResin 1.62 1.62 1.61 1.57 1.60 1.57 1.62 75108 Nafturan ® 8187 1.00 1.301.49 1.45 1.64 1.45 1.50 Expancel ® 551 0.78 1.60 — — 1.68 — — DE 20Expancel ® 461 — — 1.69 — — — — DE Dualite ® 6033 — — — 4.13 — — —Dualite ® 6032 — — — — — 4.13 — Expancel ® 091 — — — — — — 0.75 DEWinnofil ® SPT 16.20 18.42 18.33 17.88 — 17.88 18.87 Polcarb ® S — — — —18.29 — — Aerosil ® R 202 1.40 1.46 1.45 1.41 1.78 1.41 1.46 Water — —0.20 0.19 — 0.19 —

[0076] TABLE 7 Results of the measurements on the reacted sealingcompositions, which were manufactured according to the formulations oftable 6 Test Ex 9 Ex 10 Ex 11 Ex 12 Ex 13 Ref 2 Ref 3 Density [g/cm³]1.29 1.09 1.08 1.15 1.09 1.12 1.06 Tensile strength 2.64 2.55 2.26 2.212.07 1.58 1.80 [N/mm²] Elongation [%] 389 307 280 275 472 286 426 Peel14 d RT 209 125 97 94 204 209 254 [N/25 mm]

[0077] A connection was observed between the particle size of thelightweight fillers and the mechanical properties of the sealingcompositions manufactured with them. Thus it was found that a reductionin the average particle size is accompanied by an increase in thetensile strength. The average particle size of the hollow filling bodiespreferably does not exceed 40 μm. The proportion and type of the hollowfilling bodies and the mineral fillers have a substantial influence onthe mechanical properties.

[0078] Surprisingly, cured sealing compositions could be manufacturedthat have excellent mechanical properties and nevertheless an extremelylow density, in some cases of less than 1.2 g/cm³.

1. Sealing composition of low density and increased tensile strengthbased on sulfur-containing polymers, such as e.g. polysulfide, polyetherand/or polythioether, characterised in that it has a cured density of nomore than 1.3 g/cm³ determined to ISO 2781 and a cured tensile strengthof at least 1.9 N/MM2 determined to ISO
 37. 2. Sealing compositionaccording to claim 1, characterised in that it has a peel strength of atleast 90 N/25 mm.
 3. Sealing composition according to claim 1 and 2,characterised in that it has a proportion of hollow filling bodies suchas e.g. polymeric hollow spheres in the range of 0.3 to 10 wt. %. 4.Sealing composition according to one of the preceding claims,characterised in that it contains a proportion of lightweight polymericstrength-increasing fillers such as e.g. polyamide, polyethylene,polypropylene.
 5. Sealing composition according to one of the precedingclaims, characterised in that, without a proportion of hollow fillingbodies, it has a density of no more than 1.30 g/cm³.
 6. Sealingcomposition according to one of the preceding claims, characterised inthat it has hollow filling bodies with an average diameter of no morethan 50 μm, in particular of no more than 30 μm.
 7. Sealing compositionaccording to one of the preceding claims, characterised in that thehollow filling bodies have a true density in the range of 0.001 to 0.8g/cm³.
 8. Sealing composition according to one of the preceding claims,characterised in that the polymeric filler powders have a true densityin the range of 0.5 to 1.5 g/cm³.
 9. Sealing composition according toone of the preceding claims, characterised in that the inorganic fillerpowders have a true density in the range 0.18 to 4.5 g/cm³.
 10. Sealingcomposition according to one of the preceding claims, characterised inthat it additionally contains a corrosion inhibitor, in particular achromate-free corrosion inhibitor.
 11. Sealing composition according toone of the preceding claims, characterised in that it fulfilslow-temperature flexibility at −55° C. determined to ISO
 1519. 12.Sealing composition according to one of the preceding claims,characterised in that it has a peel strength of the cured sealingcomposition of at least 120 N/mm² after one thousand hours' immersion inde-ionised water at 35° C., determined to AITM 2-0013.
 13. Sealingcomposition according to one of the preceding claims, characterised inthat it has a peel strength of the cured sealing composition of at least120 N/mm² after three periods of one hundred hours each of immersion injet fuel DERD 2494 at 100° C., determined to AITM 2-0013.
 14. Sealingcomposition according to one of the preceding claims, characterised inthat it fulfils all requirements of the specifications AIMS-04-05-001and AIMS-04-05-012.
 15. Base composition based on sulfur-containingpolymers for the manufacture of a sealing composition according to oneof the preceding claims 1 to 14, characterised in that it contains atleast one long-chain linear polymer, in particular at least one linearpolysulfide with a chain length in the range approximately of 1500 to5000 g/mol and at least one short-chain branched polymer, in particularat least one branched polysulfide with a chain length in the rangeapproximately of 500 to 2000 g/mol, which has a content of trifunctionalmolecules in particular in the range of 0.1 to 5 mol. % and/or at leastone polyfunctional crosslinker with a number of functional groups n≧3.16. Base composition based on sulfur-containing polymers for themanufacture of a sealing composition according to one of the precedingclaims 1 to 14, characterised in that, before the addition of ahardener, it has a density value of no more than 1.285 g/cm³.
 17. Basecomposition according to claim 15 or 16, characterised in that it has aproportion of hollow filling bodies such as e.g. polymeric hollowspheres in the range of 0.3 to 10 wt. %.
 18. Base composition accordingto one of the preceding claims 15 to 17, characterised in that itcontains a proportion of lightweight polymeric strength-increasingfillers such as e.g. polyamide, polyethylene, polypropylene.
 19. Basecomposition according to one of the preceding claims 15 to 18,characterised in that, without a proportion of hollow filling bodies, ithas a density of no more than 1.285 g/cm³.
 20. Base compositionaccording to one of the preceding claims 15 to 19, characterised in thatit has hollow filling bodies with an average diameter of no more than 50μm, in particular of no more than 30 μm.
 21. Base composition accordingto one of the preceding claims 15 to 20, characterised in that thehollow filling bodies have a true density in the range of 0.001 to 0.8g/cm³.
 22. Base composition according to one of the preceding claims 15to 21, characterised in that the polymeric filler powders have a truedensity in the range of 0.5 to 1.5 g/cm³.
 23. Base composition accordingto one of the preceding claims 15 to 22, characterised in that theinorganic filler powders have a true density in the range of 0.18 to 4.5g/cm³.
 24. Base composition according to one of the preceding claims 15to 23, characterised in that it additionally contains a corrosioninhibitor, in particular a chromate-free corrosion inhibitor. 25.Process for the manufacture of a sealing composition according to one ofclaims 1 to 14, characterised in that at least one base polymer is mixedwith at least one adhesion promoter and the at least one lightweightfiller, in particular hollow filling bodies, is then added, a vacuumwith a residual pressure of less than 50 mbar being applied duringincorporation of the lightweight filler.
 26. Process for the manufactureof a sealing composition according to claim 25, characterised in thatthe lightweight filler is worked in in a vacuum dissolver at aperipheral toothed disc speed in the range of at least 2 m/s, inparticular at least 5 m/s, particularly preferably in the range of 12 to30 m/s.
 27. Process for the manufacture of a sealing compositionaccording to claim 25 or 26, characterised in that the other componentsof the sealing composition are then introduced and intermixed,evacuation optionally being carried out during or after this process.28. Process for the manufacture of a sealing composition according toone of claims 25 to 27, characterised in that lightweight filling bodiesand optionally also fillers with an average particle size of no morethan 30 μm, preferably of no more than 20 μm, are used, in order toachieve better spreadability and mouldability of the mouldingcomposition during working.
 29. Process for the manufacture of a sealingcomposition according to one of claims 25 to 28, characterised in thatat least one long-chain linear polymer, in particular at least onelinear polysulfide with a chain length in the range of about 1500 to5000 g/mol, is mixed with a short-chain branched polymer, in particularwith at least one branched polysulfide with a chain length in the rangeof about 500 to 2000 g/mol, which has a content of trifunctionalmolecules in particular in the range of 0.1 to 5 wt. % and/or with atleast one polyfunctional crosslinker with a number of functional groupsn≧3.
 30. Use of the sealing compositions according to claims 1 to 14 orthe base compositions according to claims 15 to 24 for the constructionand maintenance of air- and spacecraft and of motor vehicles and railvehicles, in shipbuilding, in apparatus and mechanical engineering, inconstruction and civil engineering or for the manufacture of furniture.31. Use of the products manufactured according to the process of claims25 to 29 for the construction and maintenance of air- and spacecraft andof motor vehicles and rail vehicles, in shipbuilding, in apparatus andmechanical engineering, in construction and civil engineering or for themanufacture of furniture.